1. Field of the Invention
The disclosures herein generally relate to a thermal technology for drawing an image by the application of a laser beam onto a thermal medium having a property of developing colors with heat.
2. Description of the Related Art
Rewritable technologies are becoming popular in view of their convenience and reduction in environmental burden, and various models of the rewritable technologies have been put forward. Among these rewritable models, thermal rewritable media (TRM) utilizing heat have quickly been released as commercial products and put on the market.
The related art thermal rewritable technologies generally employ a heating recording system in which thermal rewritable media are recorded on by heating with a thermal head; however, recent thermal rewritable technologies suggest that the thermal rewritable media may be heated by the application of a laser beam, as disclosed, for example, in Japanese Patent Application Publication No. 2004-90026 (hereinafter referred to as “Patent Document 1”). Such a thermal rewritable technology utilizing heat of the laser beam largely differs from the thermal rewritable technology utilizing heat of the thermal head in that the thermal rewritable technology utilizing heat of the laser beam involves contactless heating with the laser beam. In this configuration, since the laser beam is applied to the media from a distance, it may be possible to make records on movable media, such as containers being carried on a conveyor belt, by the application of a laser beam. Thus, the thermal rewritable technology utilizing the laser beam may expand its application range. Note that the recording or formation of images by the laser beam is a technology well-known in the art, which is disclosed, for example, in Japanese Patent Application Publication No. 2004-341373 (hereinafter referred to as “Patent Document 2”).
The thermal rewritable media have properties of dissipating their colors at certain temperatures and developing their colors by being heated at temperatures higher than the dissipating temperatures. However, when excessive heat is applied to the thermal rewritable media, their properties may be altered, thereby exhibiting deterioration such as a decrease in their life span or incomplete erasure of the recordings.
For example, when the laser beam having a predetermined stroke width (a stroke of a laser beam) is repeatedly applied to a same area of a thermal rewritable medium, the excessive heat may be applied to that area of the thermal rewritable medium due to the overlapped laser beam application. Examples of such an area include an “intersection”, a “turnaround” and an “approach” of the strokes (line component illustrating traces of the laser beam applied while traveling).
FIGS. 1 and 2 are diagrams illustrating examples of characters recorded by a laser beam on the thermal rewritable medium.
FIG. 1 illustrates a deformed numeral “7” (a diagonal line is added to “7”) that includes an overlapped part P1 formed of the intersection of the strokes. The overlapped part P1 of the strokes is formed by repeatedly applying the laser beam onto a part of the stroke still having residual heat that has just been formed on the thermal rewritable medium with the laser beam. As a result, the strokes on the thermal rewritable medium acquire the overlapped part P1 having a higher temperature, which may adversely affect the thermal rewritable medium.
Further, the strokes in FIG. 1 include an overlapped part P2 formed of the turnaround of the strokes. Since the turnaround of the strokes on the rewritable medium is formed by applying the laser beam for a relatively longer time due to the effect of the mirror inertia that controls an emission direction of the laser beam, the turnaround of the strokes (i.e., the overlapped part P2) on the thermal rewritable medium obtains a higher temperature, which may adversely affect the thermal rewritable medium.
FIG. 2 illustrates an example of a “radical” that is a part of components of kanji characters that is used to classify the kanji characters systematically. Note that the radical in this example appears on the left side of the kanji and indicates the meaning of “Man”. In this example, the strokes in FIG. 2 include no actually overlapped part formed by the traces of the center of the laser beam; however, an overlapped part P3 of the strokes in FIG. 2 is obtained due to the width of the laser beam.
In the thermal rewritable technology utilizing the laser beam disclosed in Patent Document 2, attempts have been made to eliminate the overlaps of the strokes by dividing, dissipating or shortening the strokes and reducing the lengths of the strokes in order to prevent the adverse effect on the thermal rewritable media. For example, if two strokes have an overlapped part, the overlapped part is eliminated by dividing, dissipating or shortening one of the strokes having an amount to be removed smaller than that of the other one. If the two strokes have the same amounts to be removed, one of the strokes subject to dividing, dissipating or shortening may be determined based on the drawing order of the strokes to be drawn (preceding or subsequent stroke to be drawn).
When the overlapped parts including a stroke width are eliminated in the above manner, a stroke sandwiched between mutually approaching two other strokes may have dissipating parts overlapped with parts of the mutually approaching two other strokes. Accordingly, a desired character or letter may not have an integrated form, which may result in degradation of drawing quality.
For example, if such overlapped parts are eliminated from the following kanji characters (a) and (b), these kanji letters may result in those illustrated in FIGS. 3A and 3B. 
FIG. 3A illustrates examples of the kanji characters from which overlapped parts are eliminated from strokes drawn in a vertical direction, and FIG. 3B illustrates examples of the kanji characters from which overlapped parts are eliminated from strokes drawn in a horizontal direction.
FIG. 4A illustrates an example of four strokes ST1 to ST4 in which the strokes ST2, St3 and ST4 partially overlap the stroke ST1. In the example of FIG. 4A, an area A1 of the stroke ST1 sandwiched between the strokes ST2 and ST3 has a size of a stroke width or less. Accordingly, the area A1 of the stroke ST1 is completely eliminated when the stroke ST1 is divided into strokes ST1-1, ST1-2 and ST1-3, without leaving any mark or trace (information) of the stroke in the area A.
Further, an area A2 of the stroke ST1 sandwiched between the strokes ST3 and ST4 has a size of the stroke width or above. Accordingly, the area A2 of the stroke ST1, though shorter than the size of the A2, has a trace of the stroke ST1 as illustrated in FIG. 4B.